Many kinds of fish are completely dependent on the sense of smell in order to find food. This in particular applies to demersal fish species which often live in environments (great depths, darkness) where odor agents dispensed from prey animals are the only signals which enable the fish to discover and localize its food. Advantage is derived from this circumstance when fishing with tackles based on bait, as for instance longline and fish pot.
Chemical analyses have shown that the concentration of odor agents dispensed from natural bait diminishes very rapidly. Measurements have been made which show that the sinking time of tackles based on bait is relatively long. A longline uses for instance about one hour in sinking down to a depth of 450 meters. This means that the bait has dispensed the essential of its odor agents before it reaches the relevant depth for catching fish, and this circumstance cannot be affected.
Different devices for dispensing odor agents under water in connection with fishing are known. U.S. Pat. No. 2,791,058 shows an elongate container having several apertures, whereby a water soluble bladder containing an odor agent is situated inside the container, so that the odor agent will trickle out while the bladder is dissolved. U.S. Pat. No. 2,922,246 also shows a container containing a bladder with odor agent. The container has an aperture at one end and a nozzle at the other end, and by being pulled in the direction of the end having the aperture the bladder will be subjected to a certain external pressure which squeezes the odor agent through the nozzle. The U.S. Pat. Nos. 4,267,658 and 4,888,907 show hollow fishing implements which are equipped with hooks and which contain agents that are attractive to fish, whereby the agents are dispensed through apertures in the implements. U.S. Pat. No. 4,267,658 shows the use of the force in a line in order to cause a certain internal pressure head in a bellows containing the agents.